Composite sheet metal article



United States Patent 6 ice The present invention relates generally toimproved metal processing and to articles formed thereby, and moreparticularly to a process for producing a unified com- ,posite metalarticle 'having distinct but integral layers of different h'ardness andductility and having distensions raised lirom one side thereof to form aseries of internal tubular passageways.

The present invention is an improvement over that disclosed inco-pending application S.N. 160,282, filed December 18, 1961, in thenames of I. Broverrnan and M. J. Pryor, now US. Patent 3,196,528. 'Ilhat application disclosed a process and articles-formed thereby wlhichcontemplated the addition of a small amount of zirconium to aluminumalloy 1100 (in accordance with the Aluminum Associations standarddesignations) to produce an aluminum-zirconium sheet having improvedphysical characteristics over the base i100 alloy. A method wasdisclosed for fabricating composite b-i-alloy articles produced tfirornthe base 1100 aluminum and the aluminumzirconium alloy. The presentapplication isdirected to improvements in processing 1100 and otheraluminum alloy sheets to produce a similar composite article without thenecessity of using any additional alloying elements in the base metal.

As is well known in the art, sheet metal panels having component layersof different hardness and ductility find considerable utility in theheatexchange field and particularly in refrigeration equipment in whichthe panels are employed as evaporators in .the freezing compartments ofsuch equipment. These e vaporatorsare formed of sheet metal panelshaving internal passageways disposed between bulged out or distendedportions of the thickness of the panel, and they are highly susceptibleto so called ice pick damage. 'Ilhis damage is caused by the use of anice pick or other sharp instrument in the course of defrosting andremoving accumulations of frost or ice from within the freezingcompartment.

This difficulty is alleviated to a surprising extent by fabricating thepanel which forms the evaporator so asto provide a partially orcompletely (flat smooth exterior surface on a lhard layer of metal, andto have the passageways formed at least predominantly or wholly fromdistensions raised only from the opposite softer, more ductile layer ofthe unified sheet forming the panel.

It is a primary concern of this invention to develop large differencesin mechanical properties between two component sheets of the same basealloy by varying the size :and distribution of particles of insolubleconstituents in the primary fabrication treatment. In this way, highstrength differentials, which are essential for producing superior oneside flat products, can be made without incurring the additional changeslfor expensive alloys 'EEOII the flat component of the composite. Also,by the'practice of the present invention there is achieved a highlydesirable and beneficial product without the attendant cost involved inadditional processing which is necessary to the addition of otheralloying elements.

In achieving the article as generally described above, certain desirableconditions exist for the formation of an effective one sidefla-tinflationpanelcontaining internal passageways, principal among thesebeing the development of an identity of physical properties duringinitial formation of the panel blank, coupied with a dissimilarity ofthese same properties during subsequent iiorrna tion of-thefinished'article from the panel blank. More specifically, it-isdesirable to maintain dimensional control and alignment of the componentsheets of the blank during initial pressure bonding which is facilitatedby a similarity of physca-l properties such as hardness andductility!between theatwocomponentsheets. On the other hand, duiingthe subsequentinflation step, to form the coolant passageways, itis desirable-that oneof the component sheets remain substantiall yorent'ir -elyundis tonted,-i.e., flat, and that the passageways befonmed'by} expansion of theother 'or softer component sheets- Ac cordingly, one of theprinciplalobjects of this invention is the provision of a process by which a pairof component sheets are fabricated and assembled .together to form acomposite blank having groups of physical characteristics which yield asubstantial differential in yield strength between the component sheetsof the composite. It is another object of the present, invention toprovide a process for making a composite metal article having componentlayers of different strength in which the component layers are formedfrom identical alloys.

It is another object, of the present invention to provide a process forfabricating a one side flat refrigerator panel.

It is another object of the present invention to provide a process offabricating a composite sheetmetal panel in which differentialproperties will develop solely from processing of the individual sheetmetal components.

It is still. another object of the present invention to provide aprocess for fabricating a composite sheet metal article having layers ofdifferent yield strength in which the layers are composed of identicalalloys which attain a final differential of physical propertieswithoutthe addition of other alloying elements.

It is a still further object of the present invention to provide a sheetmetal article having a' hard and soft component layer in whichdistensions are raised from one side thereof to form internaltubularpassageways.

Other objects and advantages of the present invention will becomeapparent from the following detailed description thereof.

vThe foregoing objects of this invention in their broadest aspect, 'areachieved to .a surprising extent by fabricating a composite sheet metalpanel having component layers thereof of different hardness by providinga pair of aluminum alloy sheets having substantially identicalcomposition, one'of the sheets having a coarse particle size dispersionof insoluble constituents present therein and .the other sheet having afine particle size dispersion of insoluble constituents present therein,forming an integrallyunified composite panel of the'sheets with portionsthereof remaining unjoined, partially annealing the comt posite panelwithina critical temperature range in which the sheet havingthecoarseparticle size dispersion underof the present invention, .analuminum base alloy is desired whichhas a major proportion ofaluminumwith minor proportions of silicon, iron, copper, manganese,magnesium and zincas impurities, either selectively or 001- atemperature within the range of 900 and 1150 F 3 lectively. The exactproportions of these impurities are not significant to the practice ofthis invention so long as they are within limits which yield alloyssusceptible to the development of dissimilar particulate precipitates ofinsoluble intermetallic compounds upon different primary heat treatment.Thus, the principles of this invention are applicable to all aluminumalloys which form stable insoluble constituents in the form ofintermetallic compounds which have a decreasing solubility rate withdecreasing temperature on primary fabrication treatment, i.e., casting,homogenization and initial breakdown hot rolling. It is, of course,vital to the practice of the invention that the intermetallic compoundsprecipitate either as a coarse particle size dispersion with largeinterparticle distance or as a fine particle size dispersion with smallinterparticle distance depending on the nature of primary fabricationtreatment. As more fully developed hereinafter, the former typedispersion favors maximum softening rates by recovery upon criticalpartial annealing after cold working, while the latter type dispersionis effective in retarding the recovery process upon subsequentfabrication treatment.

In general, due to economic and other considerations, moderate strength,common heat treatable aluminum alloys are selected as the material forboth component layers of the composite. These alloys are those havingaluminum ranging from 95.00% to 99.75% and obtain their strength throughstrain hardening, of which alloys 1100 and 3003 are typical examplesrespectively of an aluminum iron silicon group and an aluminum manganesegroup, both highly suited to the practice of this invention.

In preparing the selected alloys for processing in accordance With theprinciples of this invention, two individual masses of the same alloyare cast in accordance with conventional casting practice for thesealloys. During solidification in the casting procedure iron or iron plusmanganese may come out of solid solution, depending upon the alloycomposition selected, as the appropn' ate eutectic, While other metallicconstituents often remain in solid solution.

Following casting and scalping according to conventional practice, oneof the ingots is subjected to a homogenization treatment consisting of asoak of the ingot at for a period of 4 to 72 hours, preferably at anoptimum temperature and period within these ranges determined by thealloy selected, for example, 950-1000 F. for about hours for alloy 1100and l000-1050 F. for about 24 hours for alloy 3003. During thishomogenization treatment, the iron eutectic, if formed, is transformedto iron aluminide (FeAl in the AlFeSi group which then reacts with thesilicon to form an insoluble AlFeSi intermetallic compound which isproduced in the homogenized ingot as a coarse particulate dispersionhaving large particle size and large interparticle distance, and whichis essentially stable during subsequent hot rolling. In the aluminummanganese group, a similar coarse particulate dispersion of MnAl isformed which is also stable during subsequent hot rolling. This form ofdispersion favors maximum softening rates upon partial annealing aftercold working.

The other of the two ingots is not subjected to the aforementionedhomogenization treatment and therefore does not contain the coarseparticulate dispersion when the ingot is ready for initial breakdown hotrolling. During the subsequent hot rolling, however, aAlFeSi forms inthe AlFeSi group and MnAl forms in the AlMn group under the conjointaction of deformation and temperature. Here multisite fine dispersionswith small interparticle distance are formed which will remain stable insubsequent thermal mechanical treatment under 1000 F.

The two ingots can now be processed in an identical fashion down onRoll-Bond starting stock. In accordance with this practice,'the ingotsare hot rolledto approximately .250" gage strip, entering the rolls at,a

temperature between 800 and 1000 F., preferably at about 850 F., andthen cold rolled to .125" thickness and interannealed at about 650 to700 F. for 4 hours, or they may be initially hot rolled down to the.125" gage. During the breakdown hot rolling, the intermetallic compoundfor the selected alloy is still formed in the sheet from theunhomogenized ingot. However, due to the lower temperature range of thebreakdown hot rolling step (800 to 1000 F.) compared to that of thehomogenization range to which the other ingot was subjected, and due tothe fact that the precipitation occurs under the combined influence oflower temperature and deformation, the intermetallic compound isproduced as a fine particle size dispersion which prevents softening byrecovery in the low annealing temperature range to which the compositeis subjected following pressure Welding. In other words, this fine formof the dispersion favors minimum softening rates upon annealing aftercold work- As used in this specification, the terms fine and coarse inreference to the particle size of the intermetallic compound dispersionhave reference to those particles which are clearly resolvable or arenot resolvable by metallographic microscope techniques at magnificationsof approximately 50X.

In the production of a composite blank formed from the two alloys, asheet is taken from each of the two starting stocks and is prepared forassembly by first cleaning each of the confronting faces of thecomponents by conventional steps such as wire brushing, organic solvent,degreasing, etching in acid solutions, or similar conventional steps.

After such cleaning, a pattern of stop weld material is applied to oneor both of the confronting faces of the component by conventional means,the pattern of stop weld material being a foreshortened version in thedirection of rolling of the final pattern configuration desired. Thecomponents are then assembled together and the as sembly is tack weldedat its corners to preserve alignment of the sheets during subsequentprocessing.

Prior to pressure rolling, the assembly is heated to a temperaturewithin the range of 700 to 950 F., preferablly to about 930 F., and thenpressure rolled to about a 65% reduction to firmly weld the twocomponent sheets together in the areas not covered by the stop weldmaterial. The hot rolling is followed, after cooling, by a cold rollingreduction of about 30% to achieve the final blank gage and to producehigh strength by cold working.

After cold rolling, a large differential in yield strength of thecomponent sheets can be developed by proper partia-l annealing of theblank. The anneal is carried out in a temperature range in which thecomponent sheet fabricated from the homogenized ingot containing thecoarse particulate dispersion of insoluble constituents undergoesconsiderable loss of strength by recovery, but in which the componentsheet fabricated from the unhomogenized ingot containing the fineparticulate dispersion of insoluble constituents formed during initialhot break-down rolling undergoes only slight loss of strength byrecovery. To obtain the desired high differential in yield strength,this anneal is desirably carried out within the temperature range of 500to 620 F. for a period of 5 minutes to 10 hours and preferably at atemperature of 585 F. for about 15 minutes for alloy 1100. For alloy3003, the temperature range for partial annealing is 570 to 655 F. for asimilar period of time, with an optimum of 620 for about 15 minutes.

To illustrate the development of this differential in yield strength ithas been found that with this type of. partial annealing, fullyhomogenized 1100 Will soften to yield strength values of around 5,000psi. minimum, whereas the unhomogenized 1100 can retain strength of upto about 13,000 p.s.i. maximum, thus achieving :a differential in yieldstrength of about 8,000 p.s.i. between the components of the composite.With respect to 3003, a sheet from the fully homogenized ingot willsoften to yield strength values of around 7,000 p.s.i. minimum, whereasunhomogenized 3003 can retain strength of up to about 24,000 p.s.i.maximum, thus achieving a differential in yield strength of about 17,000p.s.i.

To complete the final article, the composite blank is inflated by thecavity die inflation technique to provide a one side flat combinationwhere the unhomogenized component becomes the flat member and willresist deformation at internal working pressures even with large tubewidths, or in the alternative by conventional inflation techniquesbetween the faces of flat platens to achieve a partial one side flatcomposite.

The following are examples of the practice of the invention and are tobe considered as illustrative and not all inclusive.

Example 1 Two individual masses of aluminum alloy 1100 containing 0.57%iron and 0.16% silicon, together with other impurities normal for thisalloy, were cast by the DC. casting process. After casting the ingotswere scalped and one of the-m was subjected to a homogenizationtreatment by heating within the temperature range of 950 to 1000 F. for16 hours. The other ingot was not homogenized but was directly subjectedto subsequent fabrication treatment identical to that performed on thehomogenized ingot. This treatment consisted of hot rolling the ingots atabout 850 F. from 16" to a thickness of 0.22", after which the sheetswere cold rolled from 0.22" to 0.125 and annealed at a temperaturebetween 650 and 700 F. for 4 hours.

Subsequently, a sample was taken from each starting stock, and a patternof stop weld material was interposed between the confronting faces ofthe sheets, after which they were assembled together, heated -to atemperature of between 930 and 950 for 20 minutes and hot rolled to areduction of 65% at this temperature, after which they were cold rolledby a reduction of about 30%. The unified sheet was then partiallyannealed at a temperature of about 585 for minutes. It was found thatthe component from the homogenized ingot softened to a yield strength ofabout 5,500 p.s.i. while the component formed from the unhomogenizedingot retained a yield strength after annealing of about 11,000 p.s.i.thereby achieving a strength differential of 5,500 p.s.i.

Example II Two individual masses of aluminum alloy 3003 containing 1.07%manganese, 0.63% iron and 0.23% silicon, together with other impuritiesnormal for this alloy, were cast by the DC. casting process. Aftercasting the ingots were scalped and one of them was subjected to ahomogenization treatment by heating Within the temperature range of 1125to 1150 F. for 16 hours. The other ingot was not homogenized but wasdirectly subjected to subsequent fabrication treatment identical to thatperformed on the homogenized ingot. This treatment consisted of hotrolling the ingots at about 850 F. from 16" to a thickness of 0.22",after which the sheets were cold rolled from 0.22" to 0.125 and annealedat a temperature between 650 and 700 F. for 4 hours.

Subsquently, a sample was taken from each starting stock, and a patternof stop weld material was interposed between the confronting faces ofthe sheets, after which they were assembled together, heated to atemperature of between 930 and 950 for 20 minutes and hot rolled to areduction of 65% at this temperature, after which they were cold roll-edby a reduction of about 30%. The unified sheet was then partiallyannealed at a temperature of about 585 for 15 minutes. It was found thatthe component from the homogenized in-got softened to a yield strengthof about 20,800 p.s.i. while the component formed from the unhomogenizedingot retained a yield achieving a strength differential of 2,700 p.s.i.

It will be apparent from the foregoing description that. there has beenprovided a method for making a composite metal article and the articleformed thereby which: is believed to provide a solution to the foregoingproblems: and achieve the aforementioned objects. It is to be under--stood that the invention is not limited to the examples" describedherein which are deemed to be merely illustrative of the best modes ofcarrying out the invention, but rather is intended to encompass all suchmodifications as are within the spirit and scope of the invention as setforth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. A composite sheet metal article comprising:

(A) a first and second component sheet having a pattern of stop weldmaterial there'between, said sheets being integrally unified except inthe area of the stop weld material;

(B) said first component sheet consisting essentially of an aluminumbase alloy having a coarse particle size dispersion of an insolubleinter-metallic compound present therein;

(C) said second component sheet consisting essentially of substantiallythe same aluminum base alloy as the first component sheet and having afine particle size dispersion of said insoluble intermetallic compoundpresent therein;

(D) said component sheets having different yield strength values, withthe first com-ponent sheet having the lower value, with distensionsraised from the first component sheet corresponding to the pattern ofstop weld material.

2. A composite sheet metal article comprising:

(A) a first and second component sheet having a pattern of stop weldmaterial therebetween, said sheets being integrally unified except inthe area of the stop weld material;

(B) said first component sheet consisting essentially of an aluminumbase alloy with Fe-l-Si 1.0% maximum and A l 99.00% to 99.75%, saidsheet having a coarse particle size dispersion of ot-AlFeSi as aninsoluble intermetallic compound present therein;

(C) said second component sheet consisting essentially of substantiallythe same aluminum base alloy as the first component sheet and having afine particle size dispersion of said insoluble intermediate compoundpresent therein;

(D) said first component sheet being relatively soft with yield strengthvalues in the order of 5,000 p.s.i. minimum and aid second componentsheet being relatively hard with yield strength values in the order of18,000 p.s.i. maximum, with distensions raised from the first componentsheet corresponding to the pattern of stop weld material.

3. A composite sheet metal article comprising:

(A) a first and second component sheet having a pattern of stop weldmaterial therebetween, said sheets being integrally unified except inthe area of the stop 'weld material;

(B) said first component sheet consisting essentially of an aluminumbase aloy with Mn 1.5% maximum and Al 95.00% to 99.00%, said sheethaving a coarse particle size dispersion of MnAl as an insolubleintermetallic compound present therein:

(C) said second component sheet consisting essentially of substantiallythe same aluminum base alloy as the first component sheet and having afine particle size dispersion of said insoluble intermetallic compoundpresent therein;

(D) said first component sheet being relatively soft with yield strengthvalues in the order of 7,000 p.s.i. minimum and said second componentsheet being relatively hard with yield strength values in the order of24,000 p.s.i. maximum, with distensions raised pattern of stop Weldmaterial.

References Cited by the Examiner UNITED STATES PATENTS Brown 29197.5

N ock 29-197.5 Steiner et a l. 29-197.5 Buckland 148-132 Peterson29-1573 Van Camp 29157.3 Wilkins 29157.3 Grenell 29197.3 X Seibel et a1748--134 X 'Wenger 29157.3 X Broverman et a1. 29157.3

HYLAND BIZOT, Primary Examiner.

2. A COMPOSITE SHEET METAL ARTICLE COMPRISING: (A) A FIRST AND SECONDCOMPONENT SHEET HAVING A PATTERN OF STOP WELD MAERIAL THEREBETWEEN, SAIDSHEETS BEING INTEGRALLY UNIFIED EXCEPT IN THE AREA OF THE STOP WELDMATERIAL; (B) SAID FIRST COMPONENT SHEET CONSISTING ESSENTIALLY OF ANALUMINUM BASE ALLOY WITH FE+SI 1.0% MAXIMUM AND AL 99.00% TO 99.75%,SAID SHEET HAVING A COARSE PARTICLE SIZE DISPERSION OF A-ALFESI AS ANISOLUBLE INTERMETALLIC COMPOUND PRESENT THEREIN; (C) SAID SECONDCOMPONENT SHEET CONSISTING ESSENTIALLY OF SUBSTANTIALLY THE SAMEALUMINUM BASE ALLOY AS THE FIRST COMPONENT SHEET AND HAVING A FINEPARTICLE SIZE DISPERSION OF SAID INSOLUBLE INTERMEDIATE COMPOUND PRESENTTHEREIN; (D) SAID FIRST COMPONENT SHEET BEING RELATIVELY SOFT WITH YIELDSTRENGTH VALUES IN THE ORDER OF 5,000 P.S.I. MINIMUM AND SAID SECONDOMPONENT SHEET BEING RELATIVELY HARD WITH YIELD STRENGTH VALUES IN THEORDER OF 18,000 P.S.I. MAXIMUM, WITH DISTENSIONS RAISED FROM THE FIRSTCOMPONENT SHEET CORRESPONDING TO THE PATTERN OF STOP WELD MATERIALL.